It is known to use a block copolymer having a hydrophilic segment and a hydrophobic segment for a drug carrier and how to charge a polymeric micelle formed by the above copolymer with a fixed drug (Japanese Patent Application Laid-Open No. 107565/1994 or U.S. Pat. No. 5,449,513). Further, know as well are a composition containing a homogeneous polymeric micelle charged therein with a water-scarcely soluble drug and a preparation method therefor (Japanese Patent Application Laid-Open No. 335267/1999).
Described in Japanese Patent Application Laid-Open No. 107565/1994 is a method in which a micelle is charged therein with a drug by forming in advance a micell of a block copolymer in an aqueous medium, adding a drug to this micelle solution and, if necessary, mixing and stirring it under heating or supersonic treatment. Further, described in Japanese Patent Application Laid-Open No. 335267/1999 is a method for preparing a micelle therein charged with a drug by dissolving a block copolymer and the drug in a water-miscible polar solvent (for example, dimethylformamide, dimethylsulfoxide and acetonitrile) and then dialyzing the solution against water.
According to the conventional techniques described above, it can be found that various advantages are present in use of polymeric micelles as drug carriers. However, there are a case where a content of a drug charged into a polymeric micelle can not be elevated so much depending on the kind of the drug, particularly a water-scarcely soluble drug and a case where a resulting polymeric micelle is not necessarily stable in water or a buffered aqueous solution.